Traditional designs of internal combustion engines permit for unwanted air pollution and loss of fuel due to evaporation of the hydrocarbon (HC) containing fuel from the tank, the carburetor, and other engine components. There is existing prior art that attempts to obviate these problems. In particular, there is an evaporative fuel control system which employs a fuel vapor collection canister containing an adsorbent material, such as activated carbon, for adsorbing evaporative fuel, and a purge system for releasing the adsorbed fuel and supplying it to the engine during operation of the engine. This evaporative fuel control system also includes a leak check system which employs different leak check methods to check for leakage of the evaporative fuel (leak of vapor) to the atmosphere.
One method by which the leak check system checks for leaks is by employing a pressure reducing pump or an electric pump, a switching valve, a reference orifice, and a pressure sensor to check leakage during stop of the engine. With this method, a reference pressure is measured after the atmosphere is vacuumed through the reference orifice by the pressure reducing pump, and a pressure within the evaporative fuel control system is measured after a certain time has elapsed after the switching valve is shifted such that a fuel tank is vacuumed or is subject to an internal negative pressure. By comparing between this measured pressure and the reference pressure, it is determined whether there is leakage larger than the reference orifice.
In one of the conventional leak check systems of the evaporative fuel control system, a pressure condition of the evaporative fuel is detected after the engine is stopped and a leak check condition is satisfied to process for initialization. In order to avoid false results, the leak check is prevented if the pressure of the evaporative fuel is more than or equal to a predetermined value. After the evaporative pressure is below the predetermined value, the leak check is carried out. Also, there are some leak check systems that avoid false check results due to an opened fuel cap during refueling. In these systems, a leak is examined with negative pressure in the evaporative fuel control system. The leak check is prevented if the pressure in the fuel tank is above a predetermined value when the vehicle is stopped. Further, there are some leak check systems that try to avoid a false check result due to an opened fuel cap during refueling by comparing a remaining amount of fuel at start of the engine with a remaining amount of fuel at last engine stop to determine whether the fuel cap is opened while the engine is stopped. If the fuel cap is opened when the engine is stopped while refueling, the leak check result is canceled to avoid a false check result due to the opened fuel cap. See JP Laid-Open No. H11-336620, JP Laid-Open No. 2002-256988, JP Laid-Open No. 2003-120437.
The check method of the conventional evaporative fuel control system is more precise than the prior method, since leakage is tested during stop of the engine during which the evaporative fuel is stable. However, in conditions where significant vaporized gas is generated due to refueling, the precision of the detection can be detrimentally affected, which leads to mistaking a no leakage condition for leakage.
On this account, JP Laid-Open No. 2003-120437 discloses a suggestion to cancel the leak check if the leak check is performed during stop of the engine and then if the refueling is detected at start of the engine.
However, without a sufficient purge of the evaporative fuel generated by the refueling after start of the engine, application of the leak check may be wrongly determined when the leak is tested again during a subsequent engine stop.